Prenatal diagnosis of placenta accreta spectrum

Placenta accreta spectrum (PAS) is a major cause of severe maternal morbidity. Perinatal outcomes are significantly improved when PAS is diagnosed prenatally. However, a large proportion of cases of PAS remain undiagnosed until delivery.The prenatal diagnosis of PAS requires a high index of suspicion. The first step is identifying maternal risk factors. The most significant risk factor for PAS is the combination of a prior caesarean delivery and a placenta previa. Other major risk factors include a prior history of PAS, caesarean scar pregnancy (CSP), uterine artery embolization (UAE), intrauterine adhesions (Asherman syndrome) and endometrial ablation.Ultrasound is the preferred imaging modality for the prenatal diagnosis of PAS and can be highly accurate when performed by a provider with expertise. PAS can be diagnosed on ultrasound as early as the first trimester. MRI may be considered as an adjunct to ultrasound imaging but is not routinely recommended. Recent consensus guidelines outline the ultrasound and MRI markers of PAS.Patients with major risk factors for PAS warrant dedicated ultrasound imaging with a provider experienced in the prenatal diagnosis of PAS.